A.J. Cole. (AP Photo/Alex Brandon)

The Nationals optioned left-handed pitcher Felipe Rivero, who was part of the return in the Jose Lobaton deal with Tampa Bay, to Class AA Harrisburg and reassigned right-handed pitching prospect A.J. Cole to minor league camp. Both will continue their spring training on the minor league side.

Cole, 22, regarded as the Nationals’ best pitching prospect outside of Lucas Giolito, was in his first Nationals big league spring training and threw well. He struck out seven and walked none in 6 2/3 scoreless innings. His fastball sits between the low and mid-90s and the Nationals are bullish on his future. But he has pitched in only three games since the start of camp because of the surplus of arms on the big league side and needs seasoning. Cole was promoted to Class AA Harrisburg late in the season and posted a 2.18 ERA over seven starts.

Rivero, 22, made three appearances in big league camp and allowed two runs over four innings. Coaches were impressed with his lively arm, but he is still developing his secondary pitches, specifically his curveball. The left-hander finished last season at High-Class A in the Tampa Bay system, posting a 3.40 ERA over 127 innings.

Major league camp is down to 55 players.